1. Field of the Invention
The present invention relates to a lens barrel that is mounted in an optical device for a camera or the like, and an imaging apparatus that includes the lens barrel.
2. Description of the Related Art
Conventionally, in a lens barrel that is used in a digital camera and the like, a mechanism that moves the lens in the direction of the optical axis is formed by a cam cylinder provided with a cam groove and a lens holder that includes a lens and cam pin, as disclosed, for example, in Japanese Patent Laid-Open No. 2008-58581. In this conventional lens barrel, when the cam cylinder rotates, the cam pin, which engaged with the cam groove on the inner circumferential side of the cam cylinder, is guided by a rectilinear key along the lift of the cam groove to move in the direction of the optical axis. Thereby, the lens holder moves in the direction of the optical axis. In addition, as can be seen in Japanese Patent Laid-Open No. 05-333255, engaging a ball in a cam grove instead of a cam pin in a mechanism that moves the lens in the direction of the optical axis has been disclosed.
However, in the lens barrel that uses a cam pin as disclosed in Japanese Patent Laid-Open No. 2008-58581, there is a case that the drive load on the lens barrel easily becomes heavy due to line contact friction between the cam pin and the cam groove when the lens is driven.
When the drive load of the lens barrel is heavy, the deceleration ratio of the deceleration gear train that transfers drive force between the motor that drives the lens barrel and the lens barrel is increased, and thus, the drive torque must be raised. In such a case, when driven by the same motor speed as the case in which the drive load of the lens barrel is light, there is a case in that the drive time for the lens barrel increases. In contrast, when a motor speed is set higher than the case in which the drive load of the lens barrel is light in order to make the drive time of the lens barrel identical to the case in which the drive load of the lens barrel is light, there is a case in that the drive noise of the lens barrel becomes loud.
In addition, in order to decrease the drive load of the lens barrel that is generated by manufacturing error, a play equivalent to the component manufacturing error may be provided in advance at the engaging portions between the cam pin and the cam groove. However, in such a case, there is a case in that the precision with which the lenses are held deteriorates. Furthermore, in a lens barrel that uses a ball as a follower instead of a cam pin, there is a concern that the ball follower may be dislocated from the cam groove due to an external force. Thus, there is a case in that, as disclosed in Japanese Patent Laid-Open No. 05-333255, locations at which a ball follower can be used become limited to portions where they are not subject to external force.